Means for determining the inclination of well pipes



Ap 1964 c. J. MCWHORTER MEANS FOR DETERMINING THE INCLINATION OF WELLPIPES 2 Sheets-Sheet 1 Original Filed June 25, 1959 F a 4 Z M. Ll. J u 0INVENTOR.

April 21, 1964 c. J. MCWHORTER MEANS FOR DETERMINING THE INCLINATION OFWELL PIPES 2 Sheets-Sheet 2 Original Filed June 25 1959 INVENTOR-ATTORNEY United States Patent- O ETERMENING THE lNCLlNATiON F WELL PIPESCullen It. McWherter, Houston, Tex assignor to Houston Oil FieldMaterial Company, Inc, Houston, Tex., a corporation of Delaware Originalapplication lune 25, 1959, Ser. No. 822,903, now Patent No. 3,039,544.Divided and this application Sept. 6, 1960, Ser. No. 59,134

5 (Claims. (Cl. 33-205) This invention relates to an apparatus forlogging wells, and more particularly means for determining variations inthe inclination of a well pipe for the purpose of locating the point atwhich the pipe is stuck in a well, and to an improved inclinometer forsuch use. This application is a division of Serial No. 822,903 filedJune 25, 1959, now Patent No. 3,039,544.

In the drilling and operation of wells, such as oil and gas wells, it iscustomary to produce a well bore by the use of a tubular drill string,having at its lower end a drill which is rotated with the string, thestring being usually of somewhat smaller external diameter than thediameter of the bore, and drilling mud being circulated through thestring and through the bore outside of the string during the drillingoperation to lubricate the drill and to carry away the cuttings formedthereby. The bore of a well produced in this manner may deviatesubstantially from the vertical and in wells of substantial depth suchdeviation frequently takes place in different directions so that thebore is curved at various locations. Under some circumstances, such aswhen the drilling takes place in inclined formations, or whenalternately soft and hard formations are encountered, the drill may bedeflected in a manner to produce relatively sharp curves or bends,sometimes referred to as dog legs.

In carrying out well drilling or other operations in wells the drillstem or other well pipe will follow generally the curvature orinclination of the bore and when the well pipe is substantially smallerin diameter than the bore, which is usually the case, the pipe engagesthe wall of the bore at various locations throughout the length of thebore, so that the inclination of the pipe varies and is different fromthe inclination of the bore at some locations and may even assume asomewhat spiral shape.

It is often desirable to determine the inclination of the well bore, orof the drill stem or other pipe therein, such as the well casing ortubing, especially for the purpose of locating a dog leg or otherirregularity in the bore likely to interfere with the insertion orwithdrawal of the well pipe, or to locate the point at which the drillstem has become stuck in the well due to caving of the formation,settling of the drilling mud, or from other causes.

Heretofore, in attempting to locate the point at which a well pipeshould be disconnected or cut olf, when such a pipe has become stuck ina well, it has been customary to make use of instruments of the straingage type, which may be lowered into the well pipe and held stationarytherein While the stress or strain on the pipe is varied to indicate bydeformation of the pipe whether the pipe at a particular location isfree or stuck. By this method it is possible to locate within roughlimits the portion of the pipe which is stuck and the portion which isfree by relatively few readings, but this method has the disadvantagethat is necessary to make a separate test at each of a large number oflongitudinally spaced locations in order to accurately locate the pointat which the pipe is stuck.

The current procedure in determining the point at which a string of pipemay be freed is to take a series of readings in the pipe at lower andlower levels until a point is found where no readings can be obtainedwhich is indicative of the fact that the stress or strain at this pointcannot be varied due to the stuck condition of pipe above lVlEANS FURice this point. Generally these readings will diminish from fullreadings in totally free pipe to zero at some point well below the topof caved in formations or settlings that are binding the pipe. This isdue to the fact that torque or tension is transmitted through the topportion of the loose material around the pipe and a certain amount offree travel is established in this loose formation by the usual workingof the pipe by the operator in an effort to free the pipe. This freetravel is often misleading as to the true degree of stuckness of thepipe and often results in the pipe being backed off or cut at a depthwell below the top of the formation that is binding it. When thishappens it is often impossible to pull the freed portion of pipe fromthe bore hole necessitating a second cut or back off, or, if the freedportion can be pulled out of the binding material the top portion of thefish may be filled by this material falling into it and future fishingoperations may be impeded.

In the inclinometer method, described more fully hereinafter, thiscondition of stress and strain transmitted through the loose formationis not so much a factor. Changes in tension and in the amount of torquepresent in free pipe will cause the pipe to repose in the bore hole indifferent conditions of convolutions and/ or spirals. This is especiallytrue if the free pipe in one condition is under a considerable tensionas shown in FIGURE 1A, and another condition of being relaxed withweight of upper sections bearing down on its as shown in FIGURE 2A.Normally, under tension the pipe would reside on the low side of thebore hole (all bore holes have some deviation from a true vertical) andgenerally conform to the contour of this low side. When undercompression, the pipe would bow out at intervals from this low side andrest approximately against the opposite wall of the bore hole. Thisproduces a series of convolutions or curves in the pipe that causes thepipe at one point to have less inclinaton and at another point to havemore inclination that it had when under tension. If there is looseformation surrounding the pipe it cannot have the freedom of side toside movement to produce changes in inclination because it would requirea very considerable force to produce side movement of the pipe againstthe restraining formation and this force is not suflicient since it isderived from the weight of upper sections applied at the relativelysmall angles in the pipe in relation to the bore hole.

Thus, if an inclinometer log is run of a section of pipe, part of whichis free and part stuck, under conditions of tension and compression,there will be a sharp change between the character of the two logs atthe point where the binding formation begins, which is the desirablepoint at which to attempt a cut or back off of the pipe. This change incharacter of the inclinometer logs in free pipe can be induced by achange in the amount of torque applied since twisting a string of pipewill cause it to assume a spiral condition with resultant changes ininclination at difierent points.

The inclinometer instrument may be used to make readings at selectedpoints like instruments currently in use, but the amount of change indeviation will vary from point to point. Any reading, however, willindicate that the pipe is free and readings can be checked at a slightlydifferent depth to avoid points where the inclination of the pipe doesnot change appreciably between conditions of tension or compression.

The present invention has for an important object the overcoming of theabove disadvantages of the methods heretofore employed in logging thevariations and inclinations of a well bore or of a pipe located in sucha bore, by the use of an improved means for continuously measuring theinclination of the bore or pipe throughout its length.

A further object of the invention is to provide an inclinometer ofimproved construction and sensitivity, for use in measuring very smallvariations in inclination from the vertical.

Another object of the invention is the provision of an inclinometerwhich is electrically operated and by which a continuous record or logof the changes in inclination of a well bore or of a pipe locatedtherein may be made.

A still further object of the invention is to provide an inclinometer ofsimple design and rugged construction whose sensitivity and accuracy issubstantially unaffected by the extreme conditions of hard usage towhich instruments of those characteristics are likely to be subjectedwhen used in well logging operations.

The above and other objects and advantages of the invention may best beunderstood from the following detailed description constituting aspecification of the same, and considered in conjunction with theannexed drawings wherein FIGURE 1 is a fragmentary, partly diagrammaticview, illustratin the method and apparatus of the invention showing theinciinometer of t e invention partly broken away and partly incross-section located in a well pipe in a well bore, the recordingmechanism employed therewith being shown diagrammatically;

FIGURE 1A is a fragmentary, vertical, central, crosssectional view on areduced scale, of a portion of a well bore showing a well pipepositioned therein, and showing a location at which the pipe is stuck inthe well, the pipe being shown in the position which it occupies duringone stage of the method of the invention;

FIGURE 2 is a fragmentary front elevational view of a portion of a chartshowing a typical form of the continuous record made by the method andapparatus of the invention, and indicating the variation in theinclination fromthe vertical of a well pipe in a well bore;

FIGURE 2A is a view similar to that of FIGURE 1A, showing the typicalvariation in the inclination of a well pipe corresponding to therecording of FIGURE 2 during another stage of the method of theinvention.

FIGURE 3 is a fragmentary, vertical, central, crosssectional view, on asomewhat enlarged scale, of a portion of a well bore, showing a wellpipe therein with the inlinometer of the invention in an operableposition in the pipe, the pipe being shown partly broken away and partlyin cross-section;

FIGURE 3A is a fragmentary, front elevational view on a somewhatenlarged scale of a portion of a chart showing a typical recordingindicating the variations of the inclinorneter of the invention as theinclinometer passes downwardly through the pipe, illustrated in FIG- URE3; and

FIGURE 4 is a vertical, central, cross-sectional view, on an enlargedscale, showing details of construction of the operating elements of theinclinometer of the invention.

Referring now to the drawings in greater detail, the method andapparatus of the invention are particularly useful in connection withthe drilling and operation of wells, such as oil wells, the bore of sucha well being indicated at B, which bore may be provided with a casing orliner C, extending downwardly from its upper end throughout a portion ofthe bore, and having an inner pipe or tubing T, of substantially smallerdiameter than the bore, which extends below the lower end of the casingC and which is illustrated as being stuck in the well bore, as by thecaving of the surrounding formation as shown at F, or the accumulationof drilling mud, sand, or the like, in the bore about the exterior ofthe pipe.

Under these conditions, it is desirable to accurately locate the zone inthe well bore in which the pipe is stuck, so that the pipe may be cut ordisconnected at a point above the stuck portion to permit the portionabove to be removed from the bore and the subsequent carrying out ofwashover operations by which the stuck portion of the pipe may berecovered from the well.

The apparatus by which the method of the invention is carried outcomprises an inclinorneter enclosed in a suitable housing itl, connectedat its upper end to the lower end of a cable 12, by which theinclinometer may be lowered into the well pipe, and which is operated bysuitable winding mechanism 14 rotatably mounted in any convenient mannerabove the upper end of the well. The cable 12 is of the conductor linetype having one or more suitably insulated conductors therein by whichelectric current may be supplied to the inclinometer and through whichcurrent may liow to suitable recording mechanism by which a continuousrecord of variations in the inclination of the well pipe may berecorded.

The inclinometer mechanism or" the invention, as best seen in FTGURES land 4 includes an elongated tubular element 16 located in the housinglid and whose upper end 18 is closed and whose lower end extends intothe upper end of an open receptacle 25) supported in the bottom of thehousing. The lower end of the tube 16 opens into the interior of thereceptacle it? in spaced relation to the bottom of the receptacle andthe tube and receptacle contain a column of a heavy liquid, preferablymercury, whose upper end is located at a predetermined level 2-in thetube caused by the pressure of air in the housing acting upon thesurface of the liquid in the receptacle. The housing ild may becompletely closed and sealed to maintain the pressure in the housing atany desired pressure and to prevent variations in the pressure of theexternal atmosphere from causing changes in the effective length of thecolumn of liquid. An inductance coil 24 surrounds the tube near itsupper end and within the tube a core 26 of magnetic material such asferrite or other suitable material having a high magnetic permeabilityis movably positioned in contact with the upper end of the mercurycolumn in position for longitudinal movement in the tube relative to theinductance or tank coil 24 to vary the inductive effect of this coil inan oscillator circuit in accordance with the longitudinal movement ofthe inductor in the tube. The coil 2-4 is connected as by means ofconductors 23 into an electrical circuit including an oscillator 30 ofconventional construction, located in the upper end of the housing 19and is in turn connected by the conductors of the cable 12 to therecorder mechanism at the surface.

The recorder mechanism may be of usual construction including a couplingtransformer 3-2, having a primary winding 3 of low impedance connectedin circuit with the oscillator 3%, through the conductors of the cable12, and with a suitable source of direct current supply, such as thatindicated at 36, and having a secondary winding 38 which is connected incircuit with a receiver 40 whose output is supplied to an electricalrecorder 42 of usual construction, which includes a chart or tape 44upon which the record is made.

The oscillator 30 is constructed to generate an alternating current at afrequency which is determined by the size of the capacitors in theoscillator and the inductance of the tank coil 24 when direct current issupplied to the oscillator from the source 36 through the primarywinding 34 of the transformer 32 and through the conductors of the cable12. The frequency of the current generated by the oscillator may be ofthe order of 40 kilocycles and this alternating current .is transmittedthrough the cable 12 to the coupling transformer 32 and through thetransformer and bypass condensers, not shown, to ground and thus back tothe oscillator. The alternating current from the oscillator issuperimposed on the direct current and generates an alternating currentof the same frequency in the secondary 3d of the coupling transformer.The direct current passing through the primary has no effect on thesecondary, so that a separation of the alternating current from thedirect current is effected by the coupling transformer in the receiver40, shown in FIGURE 1. There is another oscillator whose frequency ofoscillation may be set to equal the frequency being generated by theinstrument in the well. The receiver also includes a frequency mixingcircuit which produces no output as long as the frequency of theoscillator 30 and the frequency of the oscillator in the receiver areequal, but when one of these frequencies changes, there is generated inthe mixer device an alternating potential whose frequency is thediiference between the two frequencies being fed into the device. Thisis known as a beat frequency. This beat frequency is amplified in thereceiver and fed through a rectifier network in the receiver whichproduces a direct current output from the receiver whose magnitude isdirectly proportional to the beat frequency. The output from thereceiver is fed directly into the recorder 42, shown in FIGURE 1, whichproduces a record on the chart 4-;- indicating variations which takeplace in the frequency of the current from the oscillator 30. Thus, aslong as the frequencies of the currents, from the oscillator 39 andthose from the oscillator in the receiver remain the same, the record onthe chart 44 will be a straight line, but upon the occurrence of avariation in the frequency of the current from the oscillator 35, thedirection of the line on the chart will be changed accordingly,indicating a deviation of the inclinometer from the verti cal.

In practice, the inclinometer is suspended vertically before lowering itinto the well and the receiver 40 is adjusted to produce zero beatfrequency or zero output, and the recorder, likewise is adjusted toindicate zero, so that the pen 46 of the recorder, shown in FIGURE 1,will make a straight line longitudinally moving on the chart 44. In thisposition of the inclinometer, the effective length of the mercury columnsupporting the core 26 will be shortest, and the core will be at itsfarthest point of movement relative to the tank coil 24; causing theinductance of the tank coil to be at a minimum and the frequency of theoscillator 39 to be at a maximum.

In this condition of the apparatus, any variation of the inclinometerfrom the vertical, regardless of the direction of such deviation, willproduce a decrease in the frequency of the current from the oscillator3i} due to movement of the core 25 toward the coil 24 caused by a changein the e ective length of the mercury column, showing the pen of therecorder to move laterally on the chart 44 to indicate such change ofinclination. 1

It will be apparent that by varying the impedance in the electricalcircuit between the receiver 45 and the recorder '42, the instrument maybe calibrated to produce more or less lateral movement of the pen 46upon the occurrence of a predetermined amount of change in theinclination of the inclinometer. For example, the first calibration maybe such as to produce a vfull scale deflection of the recorder for adeviation of the inclinometer of 1 degree. Subsequent calibrations maybe made requiring a '2 degree inclination in the inclinometer to producefull scale deflection of the recorder or the instrument may becalibrated to require 3 or 4 degrees or more inclination of theinclinometer to produce full scale deflection of the recorder to adjustthe recorder to record the maximum deviation likely to be encountered ina well bore.

If this inclinometer is run in a bore hole or through a string of pipein a bore hole it is possible to record deviation from the vertical as afunction of depth as indicated in FIGURE 2. Such a recording will showsudden changes in deviation in a bore hole, commonly called dog legs,which might be missed by a directional survey made at intervals in thebore hole.

The change in the inclination of pipe as before described is necessarilysm-all because of the relatively close proximity of the walls of thebore hole to the pipe. This condition will vary as will the forcescausing changes in inclination but in general it may be stated that thechange will be of the order of 1 degree to 2 degrees or less. In someinstances of heavy sections such as drill collars, the change may be assmall as one-third of one degree. It

is apparent, therefore, that an inclinometer must be sensitive and havea high degree of resolution to successfully record such changes indeviation. As before mentioned the most sensitive calibration settingshould produce a full scale deflection of the recorder for a change ofonly one degree. On such a scale, /3 of one degree change (or 20minutes) will appear as /s of full scale which is easily discernable.

At the point where a string of pipe is stuck, it may be found that thedeviation from the vertical is relatively large as for example 9degrees. If the sensitivity calibration step is set high enough forexample 10 degrees for a full scale deflection of the recorder, then 9degrees will appear on the chart on the extreme right, and if thevariations in deviation of the pipe were only /3 of one degree, then thechanges which can be recorded in inclinometer logs between theconditions of tension and compression will appear small in comparisonwith the full cale of the log.

To offset this condition, the beat frequency oscillator in the receivermay be adjusted in a direction to reduce the beat frequency an amountequivalent to say 8 degrees; then a reading of 9 degrees will appear onthe log in the same place as a 1 degree reading would before. This willcreate an artificial zero and then by using a sensitivity step of say 2degrees for full scale, it is possible to record differentialinclinometer logs to reveal positively small changes in inclination eventhough the total inclination of the string were large.

The inherent sensitivity of this device may be seen from the fact thatthe inductance of a tank coil of an oscillator whose natural frequencyis in the order of 40 kc. has a very profound effect on the oscillator.In other words changes in the position of a tuning inductance within thetank coil will sharply change the natural frequency of oscillation.Specifically, a change of only .001 inch either in or out of the tankcoil (shown in FIGURE 4) by the inductor will shift the frequency ofoscillation by as much as 30 cycles. If an inclinometer tube 30 incheslong is inclined 1 degree from the vertical, the length of the column ofmercury will be increased .0045 inch, which will cause the inductor tomove this amount into the tankcoil and will produce 4.5 times 30, orcycles change. This will be more than 2 cycles change for each minute ofchange in deviation and easily falls within the previously describedminimum requirement of 1 degree for a full scale deflection of therecording equipment.

The inclinometer instrument will be sensitive to changes in the internaldiameter of the pipe. In FIGURE 3, the instrument moving down inside aninclined section of pipe will be disposed on the low side and the noseof the instrument will be deflected toward the center of the pipe onreaching an internal reduction in diameter, such as may be caused by acoupling 50, thus causing a momentary increase in deviation and a kickor jog on the inclinometer log away from zero. The reverse will happenas the instrument passes through such an internal reduction back intothe original pipe size, as indicated at 54. Thus internal upset pointswill show as a kick, followed by reversal. Reduction in pipe size willshow as an outward curvature of the line of the recording and anincrease in pipe size will show as an inward curvature of the line.

The inclinometer instrument may be used to find the condition at whichtension and compression are equal at a given point in a string of pipeabove the stuck point. If the instrument is positioned at a point whereit had been observed (from logs or static readings) that a change ininclination occurred between tension and compression in the pipe andstarting with a relaxed condition (compression) to slowly raise thestring of pipe at the surface until a change in reading is firstobserved; this first show of change will be at the moment tension firstarrived at the location of the instrument and will be a neutral point band will give operator sufiicient and accurate information for backingoii the pipe at this point.

It will, of course, be apparent that any suitable device, such as adirect current meter may be substituted for the recorder mechanism 42,when it is desired merely to indicate to the operator when the stuckpoint is reached without making a record of the variations ininclination of the pipe.

In carrying out the method of the invention, the inclinometer is loweredinside of the string of pipe whose variation in inclination it isdesired to determine and current is supplied to the inclinometer in themanner previously described, and the changes in inclination of theinclinometer are recorded as we show above, with the pipe in a relaxedcondition in the bore. As the inclinometer is lowered in the bore, thedeviation of the instrument from the vertical will be continuouslyrecorded on the chart When the inclinometer reaches the bottom, anupward pull may be exerted on the string of pipe, which will tend toreduce the variations in inclination throughout the tree portion of thestring, and the inclinometer may be moved upwardly through the pipewhile the pipe is maintained in this condition to make a secondrecording of the variations in inclination. By comparing the tworecordings thus produced, it will then be possible to accurately locatethe portion of the pipe which is stuck in the bore and the portion whichis free, to determine where the pipe shall be disconnected or cut off topermit the removal of the free portion. During the carrying out or" themethod in this manner, it will be apparent that the stuck portion of thepipe will be held against being affected by the upward pull exerted onthe string, so that the variations in inclination of the stuck portionwill remain substantially the same While the variations in theinclination of the free portion of the pipe will be changed, so that thelocation where the tree portion of the pipe joins the stuck portion maybe accurately located.

It will be apparent that under some conditions, the location of thestuck portion of the pipe may be determined by a single pass of theinclinometer, either with the pipe in a relaxed condition, or under thetension produced by an upward pull on the string. It will also be seenthat the amount of upward pull exerted on the string need not besuificient to place the entire length of the free portion of the pipe intension, since the method of the invention does not depend upon thetension or compression to which the pipe is subjected, but only upon thechange in inclination resulting from a change in the downward forceexerted on the pipe.

The invention is disclosed herein in connection with a certain specificembodiment of the apparatus employed and procedure in carrying out themethod, but it will be understood that these are intended by Way ofillustration only and that various changes may be made in theconstruction and arran ement of the parts of the apparatus as well as inthe particular steps of the method, within the spirit of the inventionand the scope of the appended claims.

Having thus clearly shown and described the invention, what is claimedas new and desired to secure by Letters Patent is- 1. An inclinometercomprising:

(a) an elongate liquid container,

(1)) a non-compressible liquid positioned in said container,

(c) a first gaseous pressure means acting on the top of said liquid inthe container,

(d) a second gaseous pressure means acting against the second end ofsaid liquid in the container, said second pressure means being greaterthan the first pressure means whereby the liquid has a substantiallyconstant vertical head, and

(e) an electrical means for indicating a change in the angular positionof said container relative to the vertical.

2. An inclinometer comprising:

(a) a first elongate liquid container,

(b) a second liquid container connected to one end of said elongatefirst container, said second container being of a substantially greatercross-sectional area than said first container,

(c) a non-compressible liquid positioned in said first and secondcontainers,

(d) a first gaseous pressure in said first container acting against saidliquid,

(e) a second gaseous pressure in said second container acting againstthe liquid, said second gaseous pressure being greater than said firstgaseous pressure thereby providing a substantially constant verticalhead on the liquid between said first and second gaseous pressure, and

(1) means for indicating a change in position of the upper end of theliquid relative to said first container thereby indicating a change inthe angular position of said container relative to the vertical.

3. An inclinometer comprising,

an elongate liquid container, said liquid container being closed at itstop,

a non-compressible liquid in said container,

at first gaseous pressure means acting on the top of said liquid in thecontainer,

a second gaseous pressure means acting against the bottom end of saidliquid in the container, said second pressure means being greater thanthe first pressure means whereby the liquid has a substantially constantvertical head, and

means for indicating a change in position of the upper end of the liquidrelative to said container thereby indicating a change in the angularposition of said container relative to the vertical.

4. The invention of claim 3 including a pressure tight housing about thecontainer.

5. The invention of claim 3 wherein the angular indicating means includefloat means positioned in the liquid

1. AN INCLINOMETER COMPRISING: (A) AN ELONGATE LIQUID CONTAINER, (B) ANON-COMPRESSIBLE LIQUID POSITIONED IN SAID CONTAINER, (C) A FIRSTGASEOUS PRESSURE MEANS ACTING ON THE TOP OF SAID LIQUID IN THECONTAINER, (D) A SECOND GASEOUS PRESSURE MEANS ACTING AGAINST THE SECONDEND OF SAID LIQUID IN THE CONTAINER, SAID SECOND PRESSURE MEANS BEINGGREATER THAN THE FIRST PRESSURE MEANS WHEREBY THE LIQUID HAS ASUBSTANTIALLY CONSTANTANT VERTICAL HEAD, AND (E) AN ELECTRICAL MEANS FORINDICATING A CHANGE IN THE ANGULAR POSITION OF SAID CONTAINER RELATIVETO THE VERTICAL.